Toward understanding the X-ray emission of the hard state of XTE J1550-564 Feng Yuan Collaborators: X. B. Wu (PKU), Y.Q. Xue (Purdue) , A. A. Zdziarski (CAMK) CAS Meeting, 2005, USTC

Outline Brief introduction to black hole X-ray binaries Luminous hot accretion flow (LHAF) Explaining the X-ray origin of luminous hard states with an LHAF An evidence against the jet origin of the X-ray emission in hard states

Five states (I) Quiescent state: Low/Hard state Extremely weak, L_x=10^30.5---10^33.5erg/s Nonthermal spectrum, with \Gamma=1.5-2.1(may depend on the orbital period) Low/Hard state The spectrum is dominated(>80% at 2-20 keV) by a power-law spectrum The photon index is 1.5<\Gamma<2.1 Power continuum is strong (0.1<r<0.3) Strong radio emission

Five States (II) High/soft state the disk-flux fraction is above 75%(2-20keV) The PDS shows no QPO or rms<<1% Power continuum is weak: r<0.06 No radio SPL or Very high state and intermediate state A power-law X-ray spectrum with \Gamma>2.4 is present QPO is present while the power-law contributes more than 20% of the total flux in 2-20 keV; or No QPO while the power-law contributes more than 50% of the total flux No radio, but associated with explosive formation of radio jet

Five States: spectrum Zdziarski. & Gierliński 2004

Theoretical models Esin, McClintock & Narayan 1997, ApJ

The Origin of the X-ray emission of Luminous Hard States: ADAF ? Corresponding accretion rates: The largest luminosity of ADAF: 4%L_Edd The X-ray luminosity of some luminous hard states are higher than 4%L_Edd: XTE J1550-564: 10% & 20% L_Edd GX339-4: 30% L_Edd

ADAF and Its Critical Accretion Rate The energy equation of ions in ADAFs: For a typical ADAF (i.e., ), we have: Since q- increases faster than q+ and qadv with increasing accretion rate, there exists a critical accretion rate of ADAFs, determined by (Narayan, Mahadevan & Quataert 1998): So advection is a cooling term Self-similar solution of ADAF

The dynamics of LHAFs: Basic Physics What will happen above the critical rate of ADAF? Originally people think no hot solution exists; but this is not true The energy equation of accretion flow: since: So we have:

The dynamics of LHAFs: Basic Physics An ADAF is hot because so the flow remains hot if it starts out hot. When , up to another critical rate determined by We still have:  So again the flow will be hot if it starts out hot, i.e., a new hot accretion solution (LHAFs) exists between

Properties of LHAFs Using the self-similar scaling law: LHAF is more luminous than ADAFs since it corresponds to higher accretion rates and efficiency. The entropy decreases with the decreasing radii. It is the converted entropy together with the viscous dissipation that balance the radiation of the accretion flow. Since the energy advection term is negative, it plays a heating role in the Euler point of view. The dynamics of LHAFs is similar to the cooling flow and spherical accretion flow.

Summary: four accretion solutions: accretion rates and efficiency Cool series Hot series Yuan 2001, MNRAS

Modeling the 2000 outburst of XTE J1550-564 6% LEdd 3%LEdd 1%LEdd Yuan, Zdziarski, Xue & Wu 2007, ApJ

The advection factor of the three solutions LHAF From Yuan, Zdziarski, Xue & Wu 2007, ApJ

The calculated temperature vs. the E-folding energy of the spectra Yuan, Zdziarski, Xue & Wu 2007, ApJ Temperature profiles of the three solutions; the three dots show the E-folding energy of the three X-ray spectra shown in a previous figure.

The optical and X-ray light curves of XTE J1550-564 during its 2000 outburst. Secondary maxima No maximum in the X-ray! Jain et al. 2001, ApJ

Secondary Maximum: the contribution of the jet Jet emission Yuan, Zdziarski, Xue & Wu 2007

Thank you!